Above, Meave Leakey and a colleague sift for fossils. Their teams of fossil hunters have been investigating human origins in the Turkana Basin for more than 40 years. "Place a species under stress and you can't tell what will happen," Meave Leakey said of the effect of famines and climate change in human history. "It could go extinct, or a new mutation will arise -- in this case, maybe something that led to advanced language."